Disclosed herein are the conversion of estolide compounds having unsaturated fatty acid groups into estolides containing carbonate moieties and methods of making and using the same.
The production of lubricating oils from natural products has been an area of significant study over the past couple of decades and steady incorporation of those products into the lubricant market has been made due to their good lubricity and biodegradability (Biermann, U., Angew. Chem. Int. Ed. Engl., 50: 3854-3871 (2011); Biresaw, G., et al., J. Am. Oil Chem. Soc., 80: 697-704 (2003); Wagner, H., et al., Appl. Catal., A, 221: 429-442 (2001)). Although biobased lubricants are an attractive replacement to petroleum lubricants, these natural materials suffer from performance issues due to poor cold temperature attributes, and poor oxidative and hydrolytic stabilities. To overcome these issues, vegetable oils can be chemically modified by introducing branching or reducing unsaturation in the molecule. An especially effective approach has been the development of a class of compounds known as estolides (Cermak, S., and T. Isbell, T., J. Am. Oil Chem. Soc., 78: 557-565 (2001a)). Estolides are biobased oligomeric esters obtained by the addition of a fatty acid to a hydroxyl containing vegetable oil or fat or by the condensation of a fatty acid across the olefin functionality of a vegetable oil or fat. The newly formed secondary ester groups not only makes the molecule more resistant to water hydrolysis as compared to underivatized triglycerides but also increases the branching within the molecule and dramatically improves the overall physical properties in certain applications compared to unmodified vegetable and mineral oils. In conjunction with these chemical attributes they exhibit excellent lubrication and viscosity characteristics (Cermak, S. C., et al., Ind. Crops Prod., 23: 54-64 (2006); Isbell, T. A., et al., Ind. Crops Prod., 23: 256-263 (2006)), and much improved stability toward oxidation (Cermak, S. C., and T. A. Isbell, U.S. Pat. No. 6,316,649 (2001b); Isbell, T. A., et al., U.S. Pat. No. 6,018,063 (2000)) making them useful as a basestock for functional fluid applications.
Fatty acid-based organic carbonates (aliphatic and cyclic) are an important class of compounds and exhibit interesting chemistry (Parrish, J. P., et al., Tetrahedron, 56: 8207-8237 (2000); Shaikh, A.-A. G., and S. Sivaram, Chem. Rev., 96: 951-976 (1996)) and applications including industrial fluids (Gryglewicz, S., et al., Ind. Eng. Chem. Res., 42: 5007-5010 (2003); Kenar, J. A., and I. D. Tevis, Eur. J. Lipid Sci. Technol., 107: 135-137 (2005); Kenar, J. A., et al., Journal of the American Oil Chemists' Society, 81(3): 285-291 (2004)). With regards to biobased cyclic carbonates, the 5-membered cyclic carbonate ring can be prepared from fatty ester chlorohydrins (Kenar, J. A., and I. D. Tevis, 2005) or from an epoxidized oil and carbon dioxide (Holser, R. A., Journal of Oleo Science, 56: 629-632 (2007)). In the later method, it was demonstrated that supercritical carbon dioxide was more effective than subcritical carbon dioxide to introduce the cyclic carbonate moiety onto the vegetable oils alkyl chain (Doll, K. M., and S. Z. Erhan, J. Agric. Food Chem., 53: 9608-9614 (2005b)). Although carbonated soybean oil is probably the most studied (Doll, K. M., and S. Z. Erhan, Green Chem., 7: 849-854 (2005a); Li, Z., et al., Catal Lett, 123: 246-251 (2008); Mazo, P., and L. Rios, J. Am. Oil Chem. Soc., 90: 725-730 (2013); Tamami, B., et al., J. Appl. Polym. Sci., 92: 883-891 (2004); Wilkes, G. L., et al., U.S. Pat. No. 7,045,577 (2006)), vernonia oil (Mann, N., et al., J. Am. Oil Chem. Soc., 85: 791-796 (2008)) and cottonseed oil (Zhang, L., et al., J. Am. Oil Chem. Soc., 91: 143-150 (2014)) have also been carbonated using carbon dioxide methodologies.
The ability to introduce the cyclic carbonate moiety onto other more complex biobased materials possessing unsaturation such as an estolide has not been investigated and would represent an interesting extension for this unique class of compounds. The carbonated estolides may have the advantages of the estolide structure as well as the potential chemical functionality exhibited by the cyclic carbonate group. Herein, we disclose estolide compounds containing carbonate moieties and methods of making and using the same. One example of the process is the conversion of unsaturated 2-ethylhexyl estolides into 5-membered cyclic carbonate groups through a two-step process utilizing an epoxidized estolide intermediate. The synthesis and characterization of these materials are described below.